Multi-Lumen Catheter with Enhanced Flow Features

ABSTRACT

A multi-lumen catheter including an elliptical cross-sectional profile configuration that enhances fluid flow rate while minimizing the average diameter of the catheter body is disclosed. In one embodiment the catheter includes an elongate catheter tube defining a plurality of lumens. At least a portion of the longitudinal length of the catheter tube may define an elliptical cross section, in turn defined by a major axis and a minor axis. In one embodiment, a ratio of the major axis to the minor axis of the elliptical cross section is between about 1.3 and about 1.4. The catheter body can define two, three, or more lumens. In one embodiment, a dual-lumen catheter tube includes an aspect ratio of about 1.1:1, and each lumen thereof includes an inner surface defined by a plurality of radii and an hourglass-shaped septum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 13/370,128, filed Feb. 9, 2012, and titled “Multi-Lumen Catheter Including an Elliptical Profile,” which claims the benefit of U.S. Provisional Patent Application No. 61/441,566, filed Feb. 10, 2011, and titled “Multi-Lumen Catheter Including an Elliptical Profile.” This application claims the benefit of U.S. Provisional Patent Application No. 61/651,911, filed May 25, 2012, and titled “Multi-Lumen Catheter Profile for Enhanced Flow Rate.” Each of the aforementioned applications is incorporated herein by reference in its entirety.

BRIEF SUMMARY

Briefly summarized, embodiments of the present invention are directed to a multi-lumen catheter including an elliptical cross-sectional profile configuration that enhances fluid flow rate while minimizing the average diameter of the catheter body. In one embodiment the catheter comprises an elongate catheter tube defining a plurality of lumens. At least a portion of the longitudinal length of the catheter tube defines an elliptical cross section, in turn defined by a major axis and a minor axis. A ratio of the major axis to the minor axis of the elliptical catheter tube cross section is between about 1.3 and about 1.4, in one embodiment. In another embodiment the ratio is about 1.33 in order to optimize lumen flow characteristics. The elliptical profile in one embodiment can also serve to enhance biocompatibility and kink resistance.

Though beneficially applicable to catheters of many configurations, it is appreciated that relatively thick-walled catheters, e.g., catheters including a relatively weak material such as silicone, can also benefit from the enhanced flow characteristics of the elliptic lumen profile disclosed herein. It is appreciated that the catheter body can define two, three, or more lumens, in one embodiment. In another embodiment, each lumen of a dual lumen catheter tube includes an inner surface defined by a plurality of radii and an hourglass-shaped septum.

These and other features of embodiments of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of embodiments of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the present disclosure will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. Example embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIGS. 1A and 1B are perspective and cross sectional views, respectively, of a catheter assembly configured in accordance with one embodiment;

FIG. 2 is a graph demonstrating certain operating principles of catheter assemblies described herein in accordance with one embodiment;

FIG. 3 is a cross sectional view of a catheter tube configured in accordance with one embodiment;

FIG. 4 is a cross sectional view of a catheter tube configured in accordance with one embodiment;

FIG. 5 is a cross sectional view of a catheter tube configured in accordance with one embodiment;

FIG. 6 is a cross sectional view of a catheter tube configured in accordance with one embodiment;

FIG. 7 is a cross sectional view of a catheter tube configured in accordance with one embodiment;

FIGS. 8A and 8B are perspective and cross sectional views, respectively, showing insertion and disposal of the catheter tube of FIG. 7 within an introducer, according to one embodiment;

FIGS. 9A and 9B are side and top views, respectively, of a catheter assembly in accordance with one embodiment;

FIGS. 10A and 10B are cross sectional views of the catheter assembly of FIG. 9B;

FIGS. 11A and 11B are cross sectional views of a catheter tube configured in accordance with one embodiment, both before and during fluid infusion, respectively;

FIG. 12 is a cross-sectional view of the catheter tube of FIG. 11A in a rolled-up configuration;

FIG. 13 is an end view of a catheter tube configured in accordance with one embodiment;

FIG. 14 is an end view of a catheter tube configured in accordance with one embodiment;

FIG. 15 is a top view of a catheter assembly according to one embodiment;

FIGS. 16A-16C are various cross sectional views of the catheter tube of the catheter assembly shown in FIG. 15 according to one embodiment;

FIG. 17 is a cross sectional view of a catheter tube according to one embodiment;

FIG. 18 is a cross sectional view of a catheter tube according to one embodiment;

FIGS. 19A-19C are various views showing use of a reinforcement structure in a catheter tube according to one embodiment;

FIG. 20 is a perspective view of a catheter tube reinforcement structure according to one embodiment;

FIGS. 21A and 21B show multiple positions of a catheter tube reinforcement structure according to one embodiment;

FIG. 22 is a perspective view of a distal portion of a catheter tube according to one embodiment; and

FIG. 23 is a simplified cross sectional view of the distal portion of the catheter tube of FIG. 22.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of exemplary embodiments of the present invention, and are neither limiting nor necessarily drawn to scale.

For clarity it is to be understood that the word “proximal” refers to a direction relatively closer to a clinician using the device to be described herein, while the word “distal” refers to a direction relatively further from the clinician. For example, the end of a catheter placed within the body of a patient is considered a distal end of the catheter, while the catheter end remaining outside the body is a proximal end of the catheter. Also, the words “including,” “has,” and “having,” as used herein, including the claims, shall have the same meaning as the word “comprising.”

Embodiments described herein are generally directed to a multi-lumen catheter profile configuration that enhances fluid flow rate through the lumens thereof while minimizing the average diameter of the catheter body. In one embodiment, the catheter includes an elliptical profile with a predetermined aspect ratio to enhance flow performance, biocompatibility, and/or kink resistance. In one embodiment, the aspect ratio of is about 1.3. Though beneficially applicable to catheters of many configurations, it is appreciated that relatively thick-walled catheters, e.g., catheters including a relatively weak material such as silicone, can also benefit from the enhanced flow characteristics of the elliptic lumen profile disclosed herein. The catheter body can define two, three, or more lumens, in one embodiment. In another embodiment, each lumen of a dual lumen catheter tube includes an inner surface defined by a plurality of radii and an hourglass-shaped septum.

Reference is first made to FIG. 1, which depicts a catheter assembly, generally designated at 10, configured in accordance with one embodiment. As shown, the catheter assembly (“catheter”) 10 includes an elongate catheter tube 12 formed by an outer wall 16 which, together with a septum 18 (FIG. 1B) defines two (or more) lumens 14 longitudinally extending between a proximal end 12A and a distal end 12B of the tube. A bifurcation 20 mates with the catheter tube 12 at the proximal end 12A thereof to provide fluid communication between the catheter tube and one or more extension legs 22.

FIG. 1B is a cross-sectional view of the catheter tube 12 of FIG. 1A, according to the present embodiment, wherein the catheter tube is aligned such that the width thereof extends along an x-axis and the height thereof extends along a y-axis, the x and y-axes being depicted in FIG. 1B and selected succeeding figures. As shown, the tube 12 cross-sectionally defines two lumens in a generally double-D configuration. Note that the corners 36 of each lumen 14 where the septum 18 joins with the outer wall 16 are rounded to provide more laminar flow through the lumen. The tube 12 further cross-sectionally defines an elliptical profile, further defined by a minor axis 30 parallel to the x-axis and a major axis 32 parallel to the y-axis, in the orientation shown in FIG. 1B. Both the minor and major axes 30, 32 are measured from the perimeter, or outer diameter (“OD) of the catheter tube outer wall 16 in the present embodiment. Note that, though in the present embodiment the elliptical nature of the catheter tube profile extends substantially the entire length of the tube, in other embodiments the elliptical profile can be included on less than the entire catheter tube length.

In the illustrated embodiment, the ratio between the major and minor axes 30 and 32, or aspect ratio, falls within a range that provides each lumen 14 a lumen height greater than that of lumens found in a cross-sectionally round catheter tube. This relatively increases the area of each lumen over those of a round tube, which in turn lessens the hydraulic resistance of fluid flowing through the respective lumen as seen by the following proportionality:

hydraulic resistance∝p²/A³,   (1)

where p is the lumen perimeter and A is the lumen area. In one embodiment, the aspect ratio of the major and minor axes 30 and 32 falls within a range from about 1.3 to about 1.4. In another embodiment, the aspect ratio is about 1.33. Generally, the elliptical cross sectional profile of the catheter tube 12, as shown here and in the succeeding elliptical profile configurations, enhances fluid flow characteristics, while maintaining a low average diameter for minimizing blood flow obstruction when the catheter is disposed within the vasculature of a patient. Note that in one embodiment the average diameter of the catheter is defined as the sum of catheter ODs at the major axis and the minor axis, divided by two.

The flow improvements realized by the elliptical lumen configurations shown in FIG. 1A and various other figures herein are depicted in a graph 40 of FIG. 2. In particular, graph 40 shows a bottom curve 42, middle curve 44, and an upper curve 46 that represent flow improvements as the aspect ratio of the catheter tube is increased in its elliptic nature from a round profile for each of three catheter tubes having an outer wall thickness t (indicated in FIG. 1B) equaling 10%, 15%, and 20% of the outer diameter of the catheter tube, respectively. As shown, the flow improvement for each curve 42, 44, and 46 is maximized at an aspect ratio between about 1.3 and about 1.4.

As shown by the curve 46, flow improvement is maximized for an elliptically-profiled catheter tube when the wall thickness t (see, e.g., FIG. 1B) of the catheter tube equals about 20% of the average outer catheter tube diameter. This relationship thus favors relatively thicker catheter tube walls, such as may be the case when relatively weak materials such as silicone, as employed to form the catheter tube. Note, however, that the catheter tube may be formed of any acceptable material, including polyurethanes and other thermoplastics, thermosets, etc.

Because of the elliptical nature of the catheter tube 12 as shown here, the width of the septum 18 in extending between opposite sides of the outer wall 16 to help define the two lumens 14 is shorter relative to the septum width in a correspondingly sized catheter tube with a circular cross-sectional profile. This in turn enables the septum to be stiffer in the elliptical catheter tube, which in turn helps prevent undesired septum deflection when pressure differentials exist between the lumens, such as in dialysis applications for instance. Optionally, this also enables the septum to be made thinner without compromising the rate of septum deflection over a septum of a round catheter tube.

Note that in the present embodiment shown in FIG. 1A, the bifurcation 20 provides fluid paths to establish fluid communication between the cross-sectionally round extension legs 22 and the lumens of the elliptically-shaped catheter tube 12. As such, the fluid paths defined in the bifurcation 20 in one embodiment can transition in cross-sectional shape from substantially round proximate the extension legs 22 to substantially elliptical proximate the bifurcation connection point with the proximal end 12A of the catheter tube 12. This can in turn further enhance fluid flow for the catheter assembly. In one embodiment, elliptical core pins are employed during manufacture of the bifurcation and catheter tube to provide properly shaped fluid paths within the bifurcation. The bifurcation in other embodiments can define other shaped fluid paths. Indeed, in one embodiment both the catheter tube and the extension legs can include elliptical cross-sectional shapes, and as such the bifurcation can define substantially elliptical cross-sectional fluid paths. These and other modifications are contemplated.

FIG. 3 shows a cross section of the catheter tube 12 according to another embodiment, wherein the elliptical profile is retained as defined by the minor and major axes 30, 32, but the septum 18 of the tube is slanted so as to define an angle θ with the minor axis 30. The slanted septum configuration illustrated in FIG. 3 provides in one embodiment relatively greater stability for the distal tip of the catheter during fluid infusion therethrough. This distal tip stability is at least partially due to the relatively larger product of the moment area of inertia I and the cross-sectional area A of the infusion lumen of the slanted septum configuration when compared with the product of I and A of a non-slanted septum configuration. The slanted septum configuration further balances the principal axis of I for the catheter tube, thus reducing the likelihood of the catheter tube to roll or bend in only one direction.

FIG. 4 shows a cross section of the catheter tube 12 according to another embodiment, wherein the elliptical profile is retained as defined by the minor and major axes 30, 32, but the tube defines three lumens 14A, 14B, and 14C in a triple lumen configuration. As shown, the septum 18 splits to border either side of the generally triangular third lumen 14C. As was the case with dual lumen catheter tube, the triple lumen configuration shown here improves flow rates for each of the lumens 14A, 14B, and 14C due to the elliptical catheter tube profile. It is noted that in one embodiment, one or more of the lumens 14A-14C can be configured for relatively high fluid flow rates therethrough, commonly referred to as power injection. Indeed, in the other embodiments herein described, one or more of the lumens of the catheter tube can be configured to withstand power injection.

FIG. 5 shows a cross section of the catheter tube 12 according to another embodiment, wherein the elliptical profile is retained as defined by the minor and major axes 30, 32, and the tube defines three lumens 14A, 14B, and 14C in a triple lumen configuration, as in FIG. 4, wherein the septum 18 splits to border either side of the now circular third lumen 14C. Again, and as was the case with dual lumen catheter tube, the triple lumen configuration shown here improves flow rates for each of the lumens 14A, 14B, and 14C due to the elliptical catheter tube profile.

In contrast to the configuration of FIG. 4, the catheter tube 12 in FIG. 5 includes a portion 50 defining the portions of the outer wall 16 and the septum 18 that bound the third lumen 14C. The portion 50 extends longitudinally the length of the catheter tube and includes a relatively harder material than that of the material defining the rest of the septum 18 and outer 16. This relatively harder material reinforces the third lumen 14C to enable it to withstand the high fluid pressures typically associated with power injection.

Also, in one embodiment the material included in the portion 50 enables the portions of the outer wall 16 and septum 18 thinner than what would otherwise be possible, in turn enabling the other lumens 14A and 14B to be larger than they would otherwise be. In other embodiments, the material defining the portion 50 can also be stiffer and/or include greater tensile strength relative to the other portions of the outer wall and septum so as to provide the desired characteristics for the third lumen. In yet another embodiment, the portion 50 can extend to encompass the entirety of the septum 18.

Note that, as was the case with the elliptical dual lumen configurations above, the width of the septa 18 of triple and quad lumen configurations discussed here are shorter relative to the septa in correspondingly sized catheter tubes with a circular cross-sectional profiles. Again, this stiffens the septum, which in turn helps prevent undesired septum deflection when pressure differentials exist between the lumens.

In one embodiment, for example, the catheter portion 50 includes a material of hardness of about 100 Shore A, while the remaining portions of the catheter tube 12 include a material of hardness of about 85 Shore A. Thermoplastic polyurethanes including those sold under the names TECOTHANE® and CARBOTHANE® are non-limiting examples of materials that can be configured to meet the above or other desired hardness characteristics for the portion 50 and remaining portions of the catheter tube 12. The catheter tube 12 as shown in FIG. 5 and in the other figures discussed herein can be formed via co-extrusion, insert extrusion, and other suitable methods.

Note that a catheter assembly including a catheter tube as discussed above in connection with FIGS. 4 and 5 can be employed, for instance, for dialysis procedures wherein the third lumen is configured for power injection into the patient's vasculature. However, it should be appreciated that these and the other elliptical catheter tube configurations discussed herein can be employed in a variety of catheter applications, catheter types, and lumen number/configurations.

FIG. 6 shows a cross section of the catheter tube 12 according to another embodiment, wherein the elliptical profile is retained as defined by the minor and major axes 30, 32, but the tube now defines four lumens 14A, 14B, 14C, and 14D in a quad lumen configuration. As shown, two septa 18A and 18B intersect one another to define, together with the outer wall 16, the four lumens 14A-14D. As before one, two, or more of the lumens 14A-14D can be configured for power injection and flow therethrough is optimized due to the elliptical aspect ratio of the catheter tube 12.

FIG. 7 shows a cross section of the catheter tube 12 according to another embodiment, wherein the elliptical profile is retained as defined by the minor and major axes 30, 32. A septum 58 dividing the two lumens 14 is also shown. The septum 58 is initially slackened when the catheter tube 12 is in a rest state as shown in FIG. 7. This enables the elliptical catheter tube 12 to be fed through a round catheter introducer, such as the introducer 60 shown in FIG. 8A. In particular, FIG. 8A shows that catheter tube 12 of FIG. 7 being introduced into the proximal end of the introducer 60. The introducer 60 includes a round body 62, a portion of which is initially disposed within a vessel of the patient.

Introduction of the elliptical catheter tube 12 into the round introducer body 62 forces the tube outer wall 16 to deform into the round shape of the introducer body. Because of the initially slackened state of the septum 58, the catheter tube 12 is able to be deformed from the elliptical to the circular shape when it passes into the round introducer body 62. This causes the initially slackened septum 58 to be stretched taut as the outer body 16 of the catheter tube 12 is forced into the circular shape, as shown in FIG. 8B, which shows the catheter tube 12 disposed within the introducer body 62. This enables the catheter tube 12 to be inserted into the patient's vessel, after which the introducer 60 can be removed from the vessel and the catheter tube resiliently returns to its elliptical aspect profile (FIG. 7).

In one embodiment, a proximal portion of the introducer and/or introducer body can include a transition region that gradually changes from an elliptical profile to a round profile so as to ease insertion of the initially elliptical catheter tube into the introducer. In another embodiment, an elliptical introducer may be used to place the elliptical catheter tube into the patient's vasculature. Note that the slackened shape of the septum can vary from the wavy configuration shown in FIG. 7, including a bowed or arced shaped, for instance.

FIGS. 9A and 9B show side and top views, respectively, of the catheter assembly 10 according to one embodiment, wherein the dual lumen catheter tube 12 includes a proximal portion 64 extending distally from the bifurcation 20 and a distal portion 66 extending distally from the distal termination of the proximal portion to the distal tip of the catheter tube. In particular, the proximal portion 64 of the illustrated embodiment includes a circular cross-sectional profile, as seen by the sectional view of FIG. 10A. The distal portion 66 of the catheter tube includes an elliptical cross-sectional profile, similar to the configuration shown in FIG. 1B, as seen by the sectional view of FIG. 10B.

Observation of FIGS. 9A and 9B shows that the distal portion 66 increases in diameter with respect to the proximal portion 64, best seen in the top view of FIG. 9B, owing to the elliptical nature of the distal portion. In one embodiment, this provides desirably low hydraulic resistance in the distal portion of each lumen 14, as well as enhanced power injection behavior, e.g., relatively low power injection pressures and relatively greater distal tip stability. Moreover, the round proximal portion 64 of the catheter tube of FIGS. 9A and 9B is less likely to flip when the catheter tube is maneuvered within the vasculature during and after placement procedures.

As such, it is appreciated that a portion of the catheter tube may include an elliptical profile while other portions do not. In another embodiment it is appreciated that the positions of the circular and elliptical portions of the catheter tube can be reversed. In yet another embodiment, the average diameter of the proximal or distal portion of the catheter tube can increase relative the other. More generally, the size, number, length, lumen number, and placement of one or more elliptical portions of the catheter tube can vary as appreciated by one skilled in the art. Moreover, it is understood that the nature and/or degree/magnitude of the elliptical profile can vary over the length of the catheter tube. Further details regarding catheters that include features for enhancing the stability of a distal tip thereof can be found in U.S. application Ser. No. 13/209,270, filed Aug. 12, 2011, and entitled “Trimmable Catheter Including Distal Portion Stability Features,” which is incorporated herein by reference in its entirety.

FIGS. 11A and 11B show a cross section of the catheter tube 12 according to another embodiment, wherein the two lumens 14 include an expandable profile. In particular, each lumen 14 includes an open, or patent, portion 70 proximate the septum 18 dividing the lumens and an initially collapsed portion 72 relatively farther away from the septum. At the folded, far end of each collapsed portion 72 an eyelet 74 is optionally included at a fold-point of the outer wall 16 to enhance expansion of the lumen 14 when fluid is passed therethrough. So configured, the collapsed portions 72 of the catheter tube lumens 14 define a pair of wings 76, thus giving the catheter tube 12 a “flying saucer”-like cross-sectional profile.

FIG. 11B shows the profile of the catheter 12 when one of the lumens 14 is pressurized with a pressure P, such as during power injection or other form of fluid infusion. As shown, the collapsed portion 72 expands such that the patent portion 70 and the collapsed portion combine and the overall lumen area increases. Note that the eyelet 74 enables the outer wall 16 to readily expand to accommodate the increased lumen size. When the pressure is removed, the lumen 14 returns to the original size shown in FIG. 11A. This process can be employed for either of the lumens 14, and can occur in both simultaneously. In this way, an initially low profile catheter tube (FIG. 11A) can transform in size (FIG. 11B) to accommodate relatively higher fluid flows.

FIG. 12 shows that, in one embodiment, a catheter tube, such as the catheter 12 of FIG. 11A, can be rolled in a rolled-up configuration so as to enable it to be placed in a round introducer, such as the introducer 60 shown in FIG. 8A. This enables the catheter tube to be inserted into a vessel or other body portion of the patient via use of the introducer. After insertion, the introducer can be removed from the vessel, which enables the catheter tube 12 to unroll and assume within the vessel the cross-sectional profile generally seen in FIG. 11A.

It is appreciated that the configuration of the winged catheter tube illustrated in FIGS. 11A-12 can vary in accordance with other embodiments. One example of this is shown in FIG. 13, wherein catheter tube 12 is more compact, resulting in the size of the collapsed portions 72 and corresponding length of the wings 76 being shorter relative those of the configuration shown in FIG. 11A. Yet another example is shown in FIG. 14, wherein the two lumens 14 are defined by the outer wall 16 and septum 18 so as to be positioned side-by-side, and each lumen generally defines a star-shaped or flying saucer-shaped cross-sectional profile. It should therefore be understood that these and other variations of the principles described herein are contemplated and that the cross-sectional profiles of the multi-lumen catheter tubes disclosed herein can vary as appreciated by one skilled in the art.

Reference is now made to FIG. 15 in describing aspects of a catheter assembly 110 including enhanced flow characteristics according to one embodiment. As shown, the catheter assembly (“catheter”) 110 includes an elongate catheter tube 112 formed by an outer wall 116 which, together with a septum 118 (FIG. 16A) defines two (or more) lumens 114 longitudinally extending between a proximal end 112A and a distal end 112B of the tube. A bifurcation 120 mates with the catheter tube 112 at the proximal end 112A thereof to provide fluid communication between the catheter tube and one or more extension legs 122. Each extension leg further includes a clamp 124 disposed thereon to selectively inhibit fluid flow therethrough. Note that, though shown here in a pre-curved configuration, in other embodiments, the catheter tube can be straight or assume some other shaped configuration.

FIG. 16A is a cross-sectional view of a portion of the catheter tube 112 of FIG. 15, according to the present embodiment. Note that, though in the present embodiment the cross sectional configuration shown in FIG. 16A extends longitudinally along substantially the entire length of the catheter tube, in other embodiments the cross sectional configuration can vary as a function of catheter tube length. Also, in the present embodiment, each lumen 114 is substantially identically configured in size and shape as described below; in other embodiments, however, the lumens can differ from one another and more than two lumens can be defined by the catheter tube.

In detail, FIG. 16A shows that each lumen 114 is bounded by the outer wall 116, which itself defines an outer surface or outer diameter (“OD”) described by an outer wall radius. Together with the septum 118, the outer wall 116 defines the shape and configuration of an inner surface 128 of each lumen 114. As shown, the inner surface 128 of each lumen 114 includes a first inner surface that is positioned opposite the septum 118 and is defined by a corresponding first radius r1. Adjacent either side of the first inner surface are included second inner surfaces that are defined by a corresponding second radius r2. Adjacent the second inner surfaces are included third inner surfaces that define the rounded corners 136 (FIG. 16B) of the lumen 114 and are defined by a corresponding corner radius, or third radius r3. FIG. 16A further shows that the septum 118 is centered about an axial center “c” of the catheter tube 112, is bounded on either end by the third inner surfaces, and is defined by a septum radius so as to possess an arcuate, hourglass shape.

As further shown in FIG. 16A, the magnitude of the first radius r1 of the first inner surface is greater than that of the outer wall radius of the outer wall 116. Further, the origins of the respective radii of the first radius r1 and the outer wall radius are non-concentric. Also, in the present embodiment the first radius r1 is greater than the difference: outer wall radius −t1, though other dimensional relationships between the radii are also possible.

The magnitude of the first radius r1 is greater than that of the second radius r2 of the second inner surfaces. The magnitude of the second radius r2 is greater than that of the third radius r3 of the third inner surfaces. In other embodiments, the relative magnitudes of the radii can vary from what is described herein.

The above-described lumen and radii configuration produces a maximum outer wall first thickness t1 at a point about opposite the center of the septum 118 on each lumen 114. The outer wall thins from this point to a minimum outer wall thickness t2 that is located at an angle θ from a line substantially bisecting the septum 118. The outer wall thickness again increases from t2 as it nears the septum 118. The minimized thicknesses t2 about the outer wall 116 as indicated in FIG. 16A assist in maximizing lumen area to enhance fluid flow while also providing improved kink resistance over other lumen designs. Note that the magnitude of the angle θ in the present embodiment is about 50 degrees, but can be within a range of from about 40 degrees to about 80 degrees in another embodiment. In yet other embodiments, other angles are also possible, with one factor for the angle being the catheter tube outer diameter and lumen geometry. Further, in one embodiment the minimum outer wall thickness at point t2 is less than or equal to 0.85 multiplied by the maximum outer wall thickness t1, though other relative thicknesses can be employed in the catheter tube.

Due to its hourglass shape, the septum 118 defines a minimum central first septum thickness ts1 at its center point, substantially corresponding with the catheter tube axial center c, and a maximum second septum thickness ts2 at a point substantially corresponding to a septum/wall interface 126 at either end of the septum. So configured, the septum 118 defines an arcuate lower portion of the upper lumen 114 and the arcuate upper portion of the lower lumen, in the orientation shown in FIG. 16A. In the present embodiment, the maximum septum thickness ts2 is equal to or greater than 1.4 times the central septum thickness ts1, though various other values for these measurements can be employed, including measurements that account for catheter tube outer diameter and lumen geometry.

As will be discussed below, this hourglass shape configuration of the septum 118 assists in maintaining desired fluid flow through the lumens 114, especially when differential fluid pressures exist in each lumen.

FIG. 16B shows that, in the present embodiment, the cross sectional configuration of the catheter tube 112 is elliptical such that it defines a minor axis 130 in the x-direction as indicated in FIG. 16B, and a major axis 132 in the y-direction. The aspect ratio of the major and minor axes 132/130 is about 1.1:1 in the present embodiment, though other elliptical ratios can be employed. The relatively slight elliptical nature of the catheter tube cross-sectional profile further enhances fluid flow by increasing lumen area while minimizing septum length.

In light of the above, FIGS. 16A and 16B thus show that the cross sectional profile of the catheter tube 112 includes four substantially equally configured quadrants as divided by the major and minor axes 132/130 and defined by the radii and thicknesses described above. This includes two relatively thick outer wall first thicknesses t1 and four relatively thin outer wall second thicknesses t2 of the respective lumens 114.

FIG. 16C shows that the cross sectional lumen configuration described above in connection with FIGS. 16A and 16B assists in maintaining acceptable fluid flow through the lumens 114, even when the fluid flow is pressure-differentiated, such as when one lumen is subjected to positive pressure and the other lumen is subjected to negative pressure. This situation occurs, for instance, when the catheter is employed in a hemodialysis procedure wherein blood is simultaneously being removed from and infused into the patient body via the lumens 114. As shown in FIG. 16C, when fluid flow through the lumens 114 is pressure-differentiated, the positive-pressure lumen (indicated by (+)) expands slightly by pushing the septum 118 outward. Correspondingly, the negative-pressure lumen 114 (indicated by (−)) contracts slightly, but because of its strengthening hourglass shape and maximized area per given perimeter, the septum 118 does not buckle inward into the negative-pressure lumen. This preserves a suitable amount of luminal area in the negative-pressure lumen 114 for fluid flow therethrough. Note that the catheter tube cross sectional configuration described herein is also acceptable for use in power injection operations, i.e., fluid flow through the catheter tube at pressures of about 300 psi.

In one embodiment, the catheter tube 112 includes polyurethane, though other suitable materials can be employed, including silicone, polycarbonate, etc. In yet another embodiment, it is appreciated that the cross sectional area of the catheter tube lumens can increase as a function of position along the catheter tube length while maintaining a constant tube outer diameter. For instance, the lumen areal size can be relatively small proximate the proximal end of the catheter tube, which results in a relatively thicker outer wall and hourglass-shaped septum. The lumen areal size increases toward the distal end of the catheter tube, which results in a relatively thinner outer wall and septum. This configuration can further enhance fluid flow through the catheter tube, in one embodiment. Note that this configuration is not limited to dual-lumen catheter tubes, but tubes with fewer or more lumens.

FIG. 17 shows that, in one embodiment, the catheter tube 112 can include more than one discrete material. In particular, portions of the outer wall 116 and/or septum 118 of the catheter tube 112 can include a secondary material that includes different characteristics as compared to a primary material that forms the rest of the catheter tube structure. As shown in FIG. 17, for instance, a first material 140 is employed to form the outer wall 116, while a second material 142 is employed to form the septum 118. In this embodiment, the second material 142 includes a durometer that is stiffer relative the durometer of the first material 140 forming the outer wall 116. Note that the extent of and portions of the catheter tube that are formed with the two materials can vary from what is shown and described herein.

The structure of the catheter tube 112 as depicted in FIG. 17 can be formed via a co-extrusion process, for instance, though other suitable processes can also be employed. The use of a relatively stiff second material 142 as shown in FIG. 17 can assist in strengthening the lumens of the catheter tube and resisting lumen deformation, especially when subjected to high pressure fluid flow. Further, it is appreciated that the dual material configuration of FIG. 17 can be employed together with the cross sectional lumen characteristics as described above in connection with FIGS. 16A-16C, in one embodiment. In addition, the inclusion of a second material in the catheter tube as shown in FIG. 17 enables the minimum second outer wall thickness t2 (FIG. 16A) to be disposed at locations relatively closer to the septum, if desired. Further, use of a stiffer second material for the septum can enable the septum to be thinner than what it would otherwise be while still retaining its propensity to resist septum deflection under differential pressure situations.

FIG. 18 shows that the particular cross sectional structure of the catheter tube 112 can vary while still falling within the principles described herein. As shown, the lumens 114 can be defined to present a more oval shape while the outer wall defines for each lumen a relatively thick first outer wall thickness t1, relatively thinner second outer wall thicknesses t2, and the septum 118 defining a central minimum first septum thickness ts1 and relatively thicker second septum thicknesses ts2. So configured, the radius of the inner surface of the lumens 114 opposite the septum 118 is still curved so as to be non-concentric with the radius defining the outer diameter of the outer wall 116. These and other cross-sectional catheter tube designs are therefore contemplated.

FIGS. 19A-19C show details of a reinforced catheter tube according to another embodiment, wherein a reinforcement tube 152 including an outer wall 156 and reinforcement septum 158 having a relatively stiff durometer is first provided. The top and bottom portions of the outer wall 156 opposite the reinforcement septum 158 are removed along the length of the reinforcement tube 152 to define outer wall sections 156A and 156B, as shown in FIG. 19B. Note that various processes can be followed to produce the reinforcement tube as seen in FIG. 19B.

In FIG. 19C, all or a portion of the reinforcement tube 152 is enveloped by a dual lumen catheter tube 162, such as by co-extrusion, overmolding, etc., so as to define two lumens 164. An outer cover tube 170 is disposed over the catheter tube 162 and can be heat-shrunk to bond to the catheter tube, thus forming the final catheter tube assembly. The presence of the reinforcement tube 152 in the assembly provides enhanced strength to the lumens 164, especially the septum in which the reinforcement septum 158 is disposed. This enables the catheter tube 162 to be formed from a relatively softer material than the reinforcement tube 152, which can enhance patient comfort and provide for easier catheter insertions.

FIG. 20 shows a reinforcement tube 252 according to another embodiment, including a septum 258 and an outer wall 256 that includes toothed sections 256A and 256B so as to provide relatively more flexibility than a continuous wall section. FIGS. 21A and 21B show that, in one embodiment, the reinforcement tube can include a plurality of slits 260 that cut into the outer wall 256 and septum 258. The slits 260 enable the reinforcement tube 252 of FIG. 21A to be stretched so as to assume the configuration shown in FIG. 21B. The stretched structure can then be heat-set to retain the stretched configuration before being incorporated into a catheter tube, as described above.

FIG. 22 shows that, in one embodiment, a substantially round, or elliptical catheter tube 312 similar to those described herein, can include a distal tip portion 313 that includes a substantially oval cross-sectional configuration, as seen here. In the illustrated embodiment, the oval-shaped tip portion 313 includes lumen openings 314 and side holes 318 defined through an outer wall 316. A distal hole 320 in fluid communication with one of the lumens is also included at a distal end 312B of the catheter tube 312.

As seen in FIG. 23, the oval shape of the catheter tube tip portion 313 of FIG. 22 enables the lumen openings 314 and side holes 318 to be spaced a distance apart from the walls of a vessel 330 in which the catheter tube 312 is disposed, such as a vein of the patient, for instance. This in turn helps to prevent positional occlusion of the holes caused by suck-up of the catheter tube 312 against the wall of the vessel 330 during hemodialysis and other procedures where blood is being aspirated into the catheter tube from the vessel. Of course, the particular size, shape, and configuration of the oval tip portion can vary from what is explicitly shown and described herein.

Note that the teachings herein can be applied to catheter tubes defining more than two lumens and to catheter tubes of a variety of sizes, including 14.5 Fr, 16 Fr., etc.

Embodiments of the invention may be embodied in other specific forms without departing from the spirit of the present disclosure. The described embodiments are to be considered in all respects only as illustrative, not restrictive. The scope of the embodiments is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

What is claimed is:
 1. A multi-lumen catheter assembly, comprising: an elongate catheter tube defining at least two lumens that extend between proximal and distal ends of the catheter tube, the at least two lumens defined by an outer wall and a septum having an hourglass-shaped inner surface, wherein: an outer surface of the outer wall is defined by an outer wall radius; at least one of the lumens along at least a portion of the catheter tube includes a cross-sectional profile, comprising: a first inner surface of the at least one lumen opposite the septum, the first inner surface defined by a first radius, the first radius being non-concentric with the outer wall radius; and two second inner surfaces of the at least one lumen that are each adjacent to the first inner surface and are defined by a second radius.
 2. The catheter assembly as defined in claim 1, wherein the septum defines an arcuate inner surface in the at least one lumen, the arcuate inner surface defined by a septum radius.
 3. The catheter assembly as defined in claim 1, wherein the first radius of the at least one lumen is larger relative to the outer wall radius.
 4. The catheter assembly as defined in claim 1, wherein the first radius of the at least one lumen is larger relative to the second radius.
 5. The catheter assembly as defined in claim 1, wherein the cross section of the at least one lumen further includes two third inner surfaces that are each interposed between a respective one of the second inner surfaces and the septum inner surface, the third inner surfaces each defined by a third radius that is smaller relative to the second radius.
 6. The catheter assembly as defined in claim 1, wherein the outer wall substantially includes a first material and wherein at least a portion of the septum includes a second material.
 7. The catheter assembly as defined in claim 1, wherein the catheter tube includes an elliptical cross-sectional profile with an aspect ratio of about 1.1 to
 1. 8. The catheter assembly as defined in claim 1, wherein a distal portion of the catheter tube includes a substantially oval configuration, the distal portion including a distal opening at a distal end of the catheter tube and at least two side holes.
 9. The catheter assembly as defined in claim 1, wherein the at least one lumen includes first and second lumens, each lumen including the first inner surface, the two second inner surfaces, and the inner surface of the septum.
 10. The catheter assembly as defined in claim 1, wherein the first inner surface defines a first outer wall thickness, wherein the second inner surfaces each define a second outer wall thickness, and wherein the first outer wall thickness is greater than the second outer wall thickness.
 11. A method for forming a catheter tube, the method comprising: providing a reinforcement structure that includes first and second outer wall reinforcement portions and a septum reinforcement portion; and enveloping at least a portion of the reinforcement structure within a catheter tube such that the septum reinforcement portion is disposed within a septum of the catheter tube.
 12. The method for forming as defined in claim 11, wherein the outer wall reinforcement portions are disposed on either end of the septum reinforcement portion.
 13. The method for forming as defined in claim 11, wherein enveloping at least a portion of the reinforcement structure includes extruding the catheter tube over the reinforcement structure.
 14. The method for forming as defined in claim 11, wherein enveloping at least a portion of the reinforcement structure includes completely enveloping the outer wall reinforcement portions and the septum reinforcement portion.
 15. The method for forming as defined in claim 11, further comprising: heat-shrinking an outer cover tube over the catheter tube.
 16. The method for forming as defined in claim 11, wherein the outer wall reinforcement portions include a plurality of teeth in a spaced-apart arrangement.
 17. A dual-lumen catheter assembly, comprising: an elongate catheter tube defining two lumens that extend between proximal and distal ends of the catheter tube, the two lumens defined by an outer wall and a septum, wherein an outer surface of the outer wall is defined by an outer wall radius and wherein at least a portion of a longitudinal length of each lumen includes a cross sectional profile, comprising: a first inner surface of the lumen opposite the septum that is defined by a first radius, the first radius being non-concentric with the outer wall radius; two second inner surfaces of the lumen that are each adjacent to the first inner surface and are defined by a second radius; and an arcuate septum inner surface of the lumen defined by the septum, the arcuate septum inner surface defined by a septum radius.
 18. The catheter assembly as defined in claim 17, wherein the septum defines an hourglass cross-sectional profile and wherein the catheter tube includes an elliptical cross-sectional profile with an aspect ratio of about 1.1 to
 1. 19. The catheter assembly as defined in claim 17, wherein the first radius of each lumen is larger relative to the second radius, and wherein the cross section of each lumen further includes two third inner surfaces that are each interposed between a respective one of the second inner surfaces and the septum inner surface, the third inner surfaces each defined by a third radius that is smaller relative to the second radius.
 20. The catheter assembly as defined in claim 19, wherein the first inner surface defines a first outer wall thickness, wherein the second inner surfaces each define a second outer wall thickness, and wherein the first outer wall thickness is greater than the second outer wall thickness.
 21. The catheter assembly as defined in claim 20, wherein the first radius of the first inner surface is greater than the difference of the outer wall radius minus the first outer wall thickness.
 22. The catheter assembly as defined in claim 21, wherein the at least one of the second inner surfaces defining the second outer wall thickness is disposed at an angle of about 50 degrees from a line bisecting the length of the septum.
 23. The catheter assembly as defined in claim 20, wherein at least one of the second outer wall thicknesses is less than or equal to 0.85 multiplied by the first outer wall thickness.
 24. The catheter assembly as defined in claim 17, wherein the septum includes a central first septum thickness and a second septum thickness proximate an interface of the septum with the outer wall, the second septum thickness being equal to or greater than 1.4 times the central first septum thickness.
 25. The catheter assembly as defined in claim 17, wherein a distal portion of the catheter tube includes a substantially oval configuration, the distal portion including a distal opening at a distal end of the catheter tube and at least two side holes.
 26. The catheter assembly as defined in claim 17, wherein a cross-sectional area of each lumen increases along the length of the catheter tube in a direction from the proximal end of the catheter tube toward the distal end thereof.
 27. A multi-lumen catheter assembly, comprising: an elongate catheter tube defining at least two lumens that extend between proximal and distal ends of the catheter tube, the at least two lumens defined by an outer wall and a septum having an hourglass-shaped inner surface, wherein: an outer surface of the outer wall is defined by an outer wall radius; and at least one of the lumens along at least a portion of the catheter tube includes a cross-sectional profile, comprising: a first inner surface of the at least one lumen opposite the septum, the first inner surface defined by a first radius, the first radius being non-concentric with the outer wall radius; and two lumen corners that are rounded and each defined by a corner radius. 